1. Technical Field of the Invention
The present invention relates generally to retaining boards and more particularly to locks for holding steel rule dies of varying widths within a die rule slot of a retaining board.
2. Background Art
Steel rule dies are widely used to cut a variety of materials such as cardboard and plastics into a desired shape. Often, the steel rule dies are pressure inserted into slots located in a board of wood or other suitable material. During operation of the cutter, these dies often become loosened and ultimately disengaged, thereby necessitating costly and time consuming interruption of the cutting process as repairs are undertaken. In addition, the slots are of varying widths to accommodate dies of varying widths, thus making standardization difficult.
Several attempts have been made to prevent this loosening of the steel rule dies. For example, U.S. Pat. No. 4,052,886 discloses a solid base material having caverns which are filled with semi-rigid filler material to anchor an inserted steel die. However, this method requires time-consuming filling and the ultimate strength of securing is dependant on the filler material selected. U.S. Pat. No. 3,941,038 discloses the use of S-wall shaped resilient members which pin the rule between itself and packing shims. This apparatus necessitates a difficult insertion of the rule between the resilient member and shims. A third proposal is shown in U.S. Pat. No. 3,835,746. A resilient support and spring are deformed upon insertion of the die and thereafter exert an upward force against the die to secure it in a slot. Such a deformation ultimately leads to mechanical failure of the retaining system as the dies are continuously replaced.
U.S. Pat. No. 5,029,505 discloses an apparatus for improved retention of steel rule dies inserted into slots of a retaining board. A plurality of housings, each having a spring and ball assembly, are inserted into chambers of a retaining board. The balls bias a die rule in an associated slot such that the rule is securely, yet removably, held in the slot. The apparatus is complex, however, expensive to manufacture, and requires large chambers to be cut into the retaining board. Manufacturing the spring and ball assembly inside the housing is also a complicated task.